There has been known an image display device for displaying, on a screen of a monitor or the like, an image rendering a scene of a virtual space having virtual objects disposed therein, which is viewed from a viewpoint in the line of sight. Patent Literature 1, for example, discloses a technology related to an image display device capable of accurately displaying a three dimensional image of an object with ease. In the image display device as described above, the virtual objects disposed in the virtual space specifically include, for example, the Earth represented by a plurality of polygons provided with textures of aerial photographs or satellite images, and mountain chains represented by a plurality of polygons through three-dimensional modeling.
The image display device as described above allows the user to move the viewpoint in the virtual space by performing corresponding operations, so that the user can enjoy a sense of realism as if the user is looking at the Earth from the sky.    Patent Literature 1: U.S. Pat. No. 5,912,671 A